Sweet Corn Although corn includes dent, flint, flour, and popcorn, texture, length of harvest period, storage life, and seed sweet corn (Zea mays var. rugosa) is the first thing vigor/germination requirements. that comes to mind for many Americans. Sweet corn differs from field corn in that more sugar and less starch Home gardeners can choose from numerous sweet accumulates in the kernels. The five main types of sweet corn cultivars amongst the various types. To help in corn are standard sugary (su), sugary enhanced (se), cultivar selection, the characteristics of the five types of sweet corn and suggested cultivars are provided in the shrunken-2 (sh2), synergistic (syn), and augmented supersweets (shA). These types vary in sugar content, following tables.
Genetic Types of Sweet Corn Type Characteristics Standard Sugary (su) Standard sugary cultivars have been grown for many years. These cultivars have the traditional sweet corn flavor and texture. Sugar levels are generally between 10 and 15 percent at harvest. Unfortunately, ears of sugary cultivars retain their high quality for only one or two days. Also, standard sweet corn cultivars don’t store well as sugars quickly convert to starch after harvest. Seeds germinate well at soil temperatures of 55-60°F.
Sugary Enhanced (se) Sugary enhanced cultivars contain the sugary enhancer (se) gene that produces ears with sweet, tender kernels. Sugar levels are slightly higher than standard sugary cultivars. The harvest and storage life of se types are slightly longer than standard sweet corn. Seeds germinate well at soil temperatures of 55-60°F.
Shrunken-2 (sh2) or Supersweets These cultivars contain the shrunken-2 (sh2) gene. The common name is derived from the shrunken or wrinkled appearance of the dried kernels. Shrunken cultivars have very high sugar levels. They also convert sugar to starch slowly, allowing for a longer harvest period and storage life. The seedcoats on kernels are rather thick, giving the corn a firmer, crunchy texture. Soil temperatures need to be at least 60°F for optimal germination.
Synergistic (syn) Synergistic sweet corn cultivars possess su, se, and sh2 genes. Synergistic cultivars are sweet, creamy, and tender. They have an excellent storage life. Seeds germinate well at soil temperatures of 55-60°F.
Augmented Supersweets (shA) Augmented supersweets are an improved type of shrunken sweet corn as they contain the se gene. They are sweet, tender, and have a long storage life. Soil temperatures should be at least 60°F for optimal germination.
HORT 3089 May 2018 2 Sweet Corn
Suggested Cultivars Planting Name and Type Color Season Sweet corn performs best in fertile, well-drained soils Standard Sugary in full sun. The planting site should receive at least six hours of direct sun each day. Sweet corn is a warm season Butter and Sugar Bicolor Main crop. Seeds do not germinate well when soil temperatures Early Sunglow Yellow Early are below 55°F. Seeds rot in cold, wet soils. Sweet corn Silver Queen White Late performs best in soils with a pH of 6.0-6.5. However, Sugary Enhanced sweet corn can be successfully grown in soils with a Ambrosia Bicolor Main slightly higher pH. Bodacious Yellow Main Delectable Bicolor Main Standard sweet corn cultivars may be planted in late Incredible RM Yellow Late April in central Iowa. Sugary enhanced cultivars prefer slightly warmer soil temperatures, therefore they should Luscious Bicolor Main be planted one week later than standard sweet corn. Peaches & Cream Bicolor Main Shrunken-2 and augmented supersweet cultivars should Silver King White Main not be planted until mid-May in central Iowa because Sugar Buns Yellow Main their seeds germinate poorly when soil temperatures are Sugar Pearl White Main below 60°F. Temptation Bicolor Main Trinity Bicolor Early For a continuous supply of sweet corn, plant early-, main-, Shrunken-2 and late-season cultivars or plant every 2-3 weeks. The Extra Tender 3473 White Main last practical date for planting early cultivars in Iowa is July 1. Honey ‘N Pearl Bicolor Main Northern Xtra Sweet Yellow Early Plant only fresh seed. Planting old seeds is likely to result Synergistic in poor germination and irregular plant stands. Sweet Allure Bicolor Main corn seeds are usually treated with a fungicide to reduce Café Yellow Early damping-off problems. Treated seeds are usually coated Cuppa Joe Bicolor Main with a pink or green dye for identification purposes. Illusion White Main Sow seed at a depth of one inch in heavy soils. In light, Inferno Yellow Main sandy soils, the planting depth may be two inches. Mattapoisett White Main Montauk Bicolor Main Space seeds 8-12 inches apart in rows that are 2.5-3 feet Providence Bicolor Main apart. Sweet corn also may be planted in “hills.” Sow 4-5 Sweetness Bicolor Early seeds per hill with approximately three inches between seeds. Hills should be spaced 2.5 feet apart with 2.5-3 feet Augmented Supersweets between rows. Anthem XR Bicolor Main Cumberland Bicolor Main Sweet corn is wind pollinated. To encourage pollination, Eden White Main plant several short rows or blocks rather than one or two Elle Yellow Main long rows. Poor pollination results in poorly filled ears. Nicole White Main Isolation Requirements Rosie Bicolor Main All types of corn (field corn, ornamental corn, popcorn, Takeoff Yellow Early and sweet corn) can cross-pollinate with one another. Vision Yellow Main This cross-pollination can markedly alter the sugar levels, * Season refers to the approximate days to maturity. Early cultivars mature in less texture, color, and other characteristics of sweet corn. To than 70 days, main season cultivars in 70-84 days, and late cultivars in more prevent cross-pollination and contamination, all sweet than 84 days. 3 Sweet Corn corn types should be isolated from field corn, popcorn, Apply sufficient water to moisten the upper six inches and ornamental corn. Within the sweet corn genetic of soil. The most critical periods for water are during types, shrunken-2 (sh2) cultivars should also be isolated pollination and ear development. from standard (su), sugary enhanced (se), and synergistic (syn) sweet corn types. Augmented supersweets (shA) Potential problems should be isolated from standard (su), sugary enhanced Unfavorable weather conditions (se), and synergistic (syn) cultivars. For best results, Sweet corn seeds germinate slowly in wet, cold soils, isolate sugary enhanced (se) cultivars from standard (su) resulting in poor germination and irregular plant stands. and synergistic cultivars (syn). High temperatures or drought stress during tasseling will result in poor pollination and few kernels on ears. To maintain color purity, isolate white sweet corn from yellow or bicolor sweet corn. Pollen from yellow or bicolor corn will produce yellow kernels in white cultivars. Pollen from yellow corn produces more yellow kernels in bicolor cultivars. Pollen from white sweet corn has no effect on yellow or bicolor cultivars.
Isolation can be achieved by planting different types at least 250 feet from one another. For most home gardeners this is not a practical option due to limited space. Another option is to stagger planting dates or select cultivars that mature at different times. A minimum of 14 days should separate the tasseling time of different corn types. Fertilization Insects Sweet corn requires a high level of nitrogen plus moderate The corn earworm is the most common insect pest. Corn amounts of phosphorus and potassium. Fertilizer earworm populations start to build up in early summer applications should be based on soil test results. If a soil and are usually highest from early July until mid- test has not been done, apply 2-3 pounds of a balanced September. Worm-free corn is not imperative as the tip fertilizer, such as 10-10-10, per 100 square feet. Apply the portion of the ear, where most of the damage occurs, can fertilizer uniformly over the area and incorporate it into be removed before cooking. Therefore, insecticides are the top 3-4 inches of soil just prior to planting. rarely warranted.
When the sweet corn is knee-high, apply 1-2 pounds of a balanced fertilizer (per 100 foot row) in a band along one side of each row. Plants in sandy soils may need to be side-dressed a second time just prior to tasseling. Care during the growing season Weed control and adequate moisture are essential for maximum production and quality. Shallow cultivation and organic mulches are the best ways to control weeds. Cultivation should be shallow to prevent damage to the sweet corn roots. Organic mulches conserve moisture as well as control weeds. Diseases Sweet corn requires approximately one inch of water Few serious disease problems occur on sweet corn in (either from rainfall or irrigation) per week for normal home gardens. Common smut is the most frequently development. In dry periods, water on a weekly basis. encountered disease in home gardens. Smut galls can 4 Sweet Corn develop on the stalks, leaves, ears, or tassels of sweet corn. When broken open or ripe, the galls release millions of powdery black spores. Corn smut is usually more common on plants heavily fertilized with nitrogen and those damaged by hail or mechanical means. Hot, dry weather also increases the incidence of corn smut. Control involves avoiding highly susceptible cultivars, avoiding mechanical injury to plants during cultivation, and providing adequate (but not excessive) soil fertility.
Gardeners can further minimize disease problems by purchasing seed only from reputable seed sources, using Sweet corn remains in the milk stage for a short time. crop rotation, avoiding sequential planting in adjacent In hot weather, some types of sweet corn may remain in areas, destroying crop residue, planting resistant cultivars, prime condition for only one or two days. Over mature following recommended planting dates, and fertilizing corn is tough and doughy. wisely. Many sweet corn cultivars produce two ears per plant. Animals The lower ear usually matures one or two days ahead of Raccoons, deer, and other animals can severely damage the upper one. To harvest the ears, hold the stalk below sweet corn plantings, especially when grown near wooded the ear. Twist the tip of the ear toward the ground until it areas. Raccoons and deer can be effectively deterred with breaks off. electric fencing. An electric fence consisting of two wires Standard sweet corn cultivars may lose 50 percent of positioned 6 and 12 inches above the ground effectively their sugar within 12 hours of harvest if not immediately discourages most raccoons. Two tiers of electric fencing refrigerated. Unhusked sweet corn can be stored in are often necessary to deter deer. The approximate the refrigerator at 32°F for 4-8 days. New high sugar heights of the two strands on the exterior portion of cultivars are slower to convert sugar to starch and may be the fence are 18 and 30 inches. The inner strand should harvested over a longer time period. The high sugar types be placed 50-72 inches above the ground. The fence also have a longer storage life. Sweet corn may be canned should be activated at dusk and turned off at daybreak. or frozen for year-round use. Electric fences should be used with care and caution signs installed. All fence lines must be weed free so vegetation does not touch the electric wires and short them out. How to grow “baby corn” Many cultivars are suitable for producing the immature Estimated yield baby corn that is found in salad bars and gourmet food Average yield with good management practices should be stores. However, ‘Bonus’ is a cultivar grown specifically for 11-13 ears per 10-foot row, or 10 dozen ears per 100-feet miniature ears. Baby corn is harvested when the ears are 2-4 of row. inches long and 1/3 to 2/3 inch in diameter at their base. Most sweet corn cultivars reach this stage 1-3 days after the silks Harvest and storage become visible. Experimentation is the best way to determine Sweet corn is ready to harvest approximately 15-23 days when to harvest baby corn. after the silks emerge. Sweet corn matures faster in hot weather and slower in cool weather. Revised by Ajay Nair, Cindy Haynes, and Richard Jauron, extension horticulturists. Originally prepared by Cindy Haynes, Eldon Everhart, Harvest sweet corn at the milk stage. At this stage, the and Richard Jauron, extension horticulturists. silks are brown and dry at the ear tip. When punctured with a thumbnail, the soft kernels produce a milky juice. Photos by Ajay Nair and Cindy Haynes.
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